This lesson helps introduce students to the concept that temperature causes molecules and atoms to move faster and farther apart, which in turn causes the change from solid to liquid, and liquid to gas.

Crayfish Reflexes

Most people don't pay much attention to crayfish unless they're piled high on a plate and served with melted butter. But one scientist is using the spiny crustacean to learn how social interaction can change the very chemistry of our bodies. Find out how in this Science Update.

Transcript

Could a bad day at the office rewire your brain? Don Edwards, a researcher with the Center for Behavioral Neuroscience in Atlanta, is studying crayfish to find out.

Edwards: These animals form dominance hierarchies, just like you see on the playground, or just like you see in your office -­ where there are some animals at the top and some animals at the bottom. So we've been interested in what changes occur in the nervous system when a dominance hierarchy is formed.

He says crayfish have one brain cell that makes their tails flip so they charge forward and another one makes the tail flip them into a quick retreat. After two crayfish fight, the winner's brain is rewired so he's always in "charge" mode. The loser goes into automatic reverse.

What's this got to do with people? Well, Edwards says the human and crustacean brains have more in common than you might guess. Social difficulties among people could lead to such things as anorexia or depression by causing physical and chemical changes in the brain.

Edwards: What are these different chemicals doing? How does the brain change when social conditions change? It may be that working on these animals will help us understand where to look in a higher animal so that we can address some of these other questions. For the American Association for the Advancement of Science, I'm Bob Hirshon.

Making Sense of the Research

It's hard to study the human brain directly. Aside from the ethical problems with opening up people's skulls and studying their brains, our nervous systems are so complex and intricate that it's difficult to answer simple questions about how they work. It's kind of like trying to teach first-graders about spelling and grammar by making them read Hamlet.

That's why brain researchers often like to study very simple creatures, like flatworms, lamprey eels, and in this case, crayfish. The nervous system of the crayfish is actually rather large, making it possible to individually identify cells and attribute them to particular patterns of behavior—in this case, the tendency to attack or escape when confronted. This, combined with the large body of existing data on the crayfish, make this crustacean an ideal subject for behavioral research.

The specific behavior examined in this study is the crayfish's signature tail flip. The crayfish flips its tail forward when it wants to be aggressive, or backward when it wants to retreat. When two crayfish meet, they fight to establish dominance. One assumes a dominant role, the other a subordinate role, evidenced by the use of either a forward or backward tail flip. Once established, they'll keep these roles until a new interaction occurs. This dominance hierarchy keeps the crayfish from having to constantly fight to establish who's boss, because they will maintain these roles until they meet other crayfish, at which time conflict arises and new roles are established.

Edwards' findings suggest that these patterns of behavior actually rewire the brain, solidifying these behaviors until the brain is again rewired through another social interaction. What's more, he's found that these behavioral changes can influence the production of a brain chemical called serotonin.

In humans, changes in serotonin levels are associated with a number of chronic psychological problems, like clinical depression and eating disorders. These are disorders in which people fall into habits that are difficult to break out of, and they're often treated with medications that try to alter their serotonin levels directly. But the crayfish research suggests another approach: if patients can find ways to change their behavior, perhaps their serotonin levels will change as a result of that. Of course, it's a long way from crayfish to people—but it's a start.

Now try and answer these questions:

Dr. Edwards mentions the idea of a dominance hierarchy. How might this manifest itself with other animals? What about people?

How are the roles in these hierarchies established? Can they be reset? How?

What are some aggressive and escape behaviors that are exhibited in other animals? What about humans?

Why study crayfish?

What is serotonin? What does that have to do with the crayfish research? How might it apply to humans?

Do you think that humans might experience something similar to the crayfish: that single experiences can create long-lasting changes in behavior patterns? Do you think this can ever be a good thing? Can you think of any examples?

To read more about Dr. Edwards' work, visit his homepage. Here, you can read more about crayfish behavior, explore other reference sources, or view a photo of the crayfish tail flip referred to in this Science Update.